1. Field of the Invention
The present invention relates to measuring properties of fluids. The invention is particularly suited for measuring properties of reservoir fluids involved in enhanced oil recovery. Such properties being, by way of example, phase equilibria, phase volumes, compositions, densities, viscosities, and interfacial tensions of fluids.
2. Description of the Prior Art
Multicomponent, multicontact phase behavior data on reservoir fluids are necessary for complete modeling of multicontact phase behavior which occur in miscible displacement processes. The typical experiment in the past has involved mixing of components in a single equilibrium cell. The contents are mixed by shaking or stirring and allowed to equilibrate by diffusion and convection. Samples of lower and upper phases are removed from the cell through taps, and their compositions are analyzed. For multicomponent systems in windowed cells, phase volumes are measured visually and compositions can be measured by refractive index. Phase densities and viscosities must be measured in separate experiments.
Franklin M. Orr and Matthew K. Silva, "Equilibrium Phase Compositions of CO.sub.2 -Hydrocarbon Mixtures: Measurement by a Continuous Multiple Contact Experiment," presented at the Third Joint SPE/DOE Symposium on Enhanced Oil Recovery, April 4-7, 1982, Tulsa, Okla., reports an apparatus for measuring phase equilibria, densities, viscosities, and interfacial tensions. Orr et al describes a continuous multicontact experiment (CMC) in which fluids are continuously injected, circulated and withdrawn. The CMC experiment can potentially produce data in a time short relative to the single contact cell. The major drawbacks of the CMC are that the system composition is never known exactly, there is no measurement of phase volumes, and relatively large samples must be removed for analysis and no more than two phases can be sampled.
Ralph Simon, "A Visual System for Measuring the Properties of Petroleum Reservoir Fluids," presented at the Annual AlChE Meeting, New Orleans, La., Nov. 8-12, 1981, reports an apparatus based on using a sapphire cell. The system is operable up to 20,000 psi and 400.degree. F. All measurements except compositions are performed with the fluid remaining in the cell: density by gamma ray transmission, viscosity by torsional crystal vibration, interfacial tension by pendant drop and photon correlation spectroscopy, phase volumes by visual observation, and compositions by gas chromatography. A drawback in the design is that mercury is used as the pressure fluid; therefore, the system cannot be used for high carbon dioxide containing fluids because of mercury/CO.sub.2 emulsion formation.